The present invention relates to the field of transformer fabrication. More particularly, it relates to transformers made by printed circuit board techniques.
Transformers are devices that increase or decrease the voltage of alternating current. They are usually fabricated by winding several coils of wire around a large magnetic core. Cores may be cylindrical but typically, toroidal core are used. One coil, called the primary, is connected to the input circuit, whose voltage is to be changed. The other coil, called the secondary, is connected to the output circuit, which is where the electricity with the changed (transformed) voltage is used.
As the alternating current in the input circuit travels through the primary, it sets up a magnetic field that changes in intensity and direction in response to the alternating current. The changing magnetic flux induces an alternating voltage in the secondary. The ratio of the number of turns in each coil determines the transformation ratio. For example, if there are twice as many turns in the primary as in the secondary, the output voltage will be half that of the input voltage. On the other hand, since energy cannot be created or destroyed, the output current will be twice as much as the input current.
Since coil winding is a long and tedious process, commercial transformer design is primarily driven by cost. In other words, manufacturers try to minimize core size and coil length. However, there is a practical limit to decreasing the size of transformers and the smallest transformers, which would be desirable for high frequency applications, are very expensive to produce. The reduction in size usually reduces cost through the lesser amount of material needed to build them but this cost of materials, usually assumed to be a major portion of total cost, is a lesser factor as size goes below a practical limit. Continued reduction in size increases cost of assembly exponentially as size continues to get smaller until, at some minimum size, a smaller size cannot be produced. The result is that commercially available transformers are only 90 to 95 percent efficient.
If a way could be found to fabricate transformers that did not require coil winding, that was inexpensive, and that produced small transformers, with higher efficiency, it would satisfy a long felt need in the field of transformer fabrication. This breakthrough would facilitate use of transformers in high frequency applications.